A user interface allows a person (a user) to interact with a particular machine, device, computer program or other complex tool. Typically a user interface provides a way for the user to input information and a way for the machine to provide information back to the user (i.e., for the machine to provide output). Input typically allows the user to manipulate the system while output allows the system to convey the effect(s) of the user's manipulation.
Two common types of computer user interfaces are graphical user interfaces and web-based user interfaces. A graphical user interface or GUI is a type of user interface that allows a user to interact with a computer and computer-controlled devices by presenting graphical icons, visual indicators or graphical elements, sometimes in conjunction with text, labels or text navigation, to represent information and actions available to the user. Instead of offering only text menus, or requiring typed commands, an action is usually performed through direct manipulation of graphical interface elements called controls.
A control is an interface element with which the user interacts, such as a window, a button or a text box. A control provides a single interaction point for the direct manipulation of a particular kind of data. Controls are also visual basic building blocks which, when combined in an application, hold the data processed by the application and control the available interactions on the data.
A second common type of user interface is the web-based user interface. A web-based user interface accepts input and provides output by generating web pages which are transmitted via the Internet and viewed by the user using a web browser program. Newer implementations utilize Java, AJAX, Adobe Flex, Microsoft .NET, or similar technologies to provide realtime control in a separate program, eliminating the need to refresh a traditional HTML-based web browser.